On Mon, 2015-07-27 at 16:49 +0100, Robin Murphy wrote:
> On 27/07/15 16:31, Russell King - ARM Linux wrote:
> > On Mon, Jul 27, 2015 at 02:23:26PM +0100, Robin Murphy wrote:
> >> On 16/07/15 10:04, Yong Wu wrote:
> >>> This patch adds support for mediatek m4u (MultiMedia Memory Management
> >>> Unit).
> >>>
> >>> Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> >> [...]
> >>> +static void mtk_iommu_flush_pgtable(void *ptr, size_t size, void *cookie)
> >>> +{
> >>> + struct mtk_iommu_domain *domain = cookie;
> >>> + unsigned long offset = (unsigned long)ptr & ~PAGE_MASK;
> >>> +
> >>> + dma_map_page(domain->data->dev, virt_to_page(ptr), offset,
> >>> + size, DMA_TO_DEVICE);
> >>
> >> Nit: this looks like it may as well be dma_map_single.
> >>
> >> It would probably be worth following it with a matching unmap too, just to
> >> avoid any possible leakage bugs (especially if this M4U ever appears in a
> >> SoC supporting RAM above the 32-bit boundary).
> >
> > Why not do the job properly? Take a look at how I implemented the
> > streaming DMA API on Tegra SMMU (patch set recently sent out earlier
> > today).
> >
> > There's no need for hacks like dma_map_page() (and discarding it's
> > return value) or dma_map_page() followed by dma_unmap_page().
>
> Indeed, as it happens I do have a branch where I prototyped that for the
> long-descriptor io-pgtable-arm code a while ago; this discussion has
> prompted me to dig it up again. Stay tuned, folks...
Hi Russell, Robin,
From I see in arm-smmu-v3.c in v4.2-rc1,
The flush_pgtable seems like this:
//==========
dma_addr_t dma_addr;
dma_addr = dma_map_page(dev, ptr, size, DMA_TO_DEVICE);
if (dma_mapping_error(dev, dma_addr))
dev_err(dev, "failed to flush pgtable at %p\n", ptr);
else
dma_unmap_page(dev, dma_addr, size, DMA_TO_DEVICE);
//==========
I will change map like this and use dma_map_single instead.
Is this also seems to be not proper?
Then how to do it? add this before unmap? :
dma_sync_single_for_device(dev, dma_addr, size, DMA_TO_DEVICE);
>
> Robin.
>
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